Add a pre-generation hook to avoid non-lowercase slugs - fixes #2042

hooks/pre_gen_project.py

@@ -22,6 +22,10 @@ if hasattr(project_slug, "isidentifier"):
         project_slug.isidentifier()
     ), "'{}' project slug is not a valid Python identifier.".format(project_slug)
 
+assert (
+    project_slug == project_slug.lower()
+), "'{}' project slug should be all lowercase".format(project_slug)
+
 assert (
     "\\" not in "{{ cookiecutter.author_name }}"
 ), "Don't include backslashes in author name."

tests/test_cookiecutter_generation.py

@@ -2,6 +2,7 @@ import os
 import re
 
 import pytest
+from cookiecutter.exceptions import FailedHookException
 from pytest_cases import pytest_fixture_plus
 import sh
 import yaml
@@ -145,3 +146,14 @@ def test_travis_invokes_pytest(cookies, context):
             assert yaml.load(travis_yml)["script"] == ["pytest"]
         except yaml.YAMLError as e:
             pytest.fail(e)
+
+
+@pytest.mark.parametrize("slug", ["project slug", "Project_Slug"])
+def test_invalid_slug(cookies, context, slug):
+    """Invalid slug should failed pre-generation hook."""
+    context.update({"project_slug": slug})
+
+    result = cookies.bake(extra_context=context)
+
+    assert result.exit_code != 0
+    assert isinstance(result.exception, FailedHookException)